Liquid fuels such as diesel and, more recently, gaseous fuels have been used to fuel vehicle engines for many years now. Such gaseous fuels include, among others, natural gas, propane, hydrogen, methane, butane, ethane or mixtures thereof. The engine fuel injection system generally comprises a plurality of fuel injectors fluidly connected to a fuel supply conduit. Generally, in the case of a direct injection system, each fuel injector is located in a bore formed in the cylinder head of the engine and the fuel supply conduit, commonly referred to as the fuel rail, can be either located in a bore formed in the cylinder head or can be an external pipe which is fluidly connected to each of the injectors through bores provided in the cylinder head. Each injector operates as a fuel valve which opens and closes to inject fuel into the combustion chamber of each engine cylinder and respectively, to stop fuel flow into the combustion chamber. Such opening and closing of the fuel injectors generates pressure pulsations at the injector fuel inlet which cannot be dampened during the time the injector is closed because of the short interval between the injection events. Such pressure pulsations can generate a fuel pressure increase or a pressure drop at the injector nozzle which affects the amount of fuel injected into the combustion chamber during an injection event. Such pressure pulsations can also be transmitted from one injector back to the fuel rail and through the rail to the next fuel injector of the engine. Furthermore, if the pressure in the fuel rail fluctuates the pressure pulsations in the rail can be transmitted to the inlet of the fuel injector and further to the injector nozzle.
In the past, the problem described above has been addressed by incorporating a bush in the fuel rail which supplies fuel to an injector of diesel engine, as described for example in U.S. Pat. No. 7,516,734, such bush providing an orifice which restricts fuel flow from the fuel rail to the injector, thereby dampening the pressure pulsations in the fuel passage which connects the fuel rail to the fuel injector. Several other similar solutions have been disclosed in the prior art to address the problem of pressure pulsations in conventional liquid fuels such as diesel fuel or gasoline supplied to an injector of an internal combustion engine. In gaseous fuels, the pressure pulsations caused by the opening and closing of the injectors behave differently than in liquid fuels, because of the physical composition of the gaseous fuel which tends to prolong the pressure oscillations.
In other variants, at least one dampening element is disposed in an opening of the fuel injector through which fuel flows from the fuel rail such as described in U.S. Pat. No. 7,059,548.
The design solutions presented in the prior art do not consider the problem of determining the location of the pulsation dampening orifice relative to the injector nozzle for controlling the dampening of the pressure pulsations between the fuel rail and the fuel injector and for controlling the fuel pressure within the nozzle chamber before fuel is injected into the combustion chamber. This problem becomes even more relevant for dual fuel engines which inject a gaseous fuel and a liquid fuel directly into the combustion chamber through a dual fuel injection valve which comprises a dual needle assembly having concentric needles for separately and independently injecting the liquid fuel and the gaseous fuel, as described for example in applicant's U.S. Pat. No. 7,124,959. In such fuel injectors a predetermined bias has to be maintained between the liquid fuel pressure and the gaseous fuel pressure within the body of the injector, with the liquid fuel pressure being higher than the gaseous fuel pressure, to prevent gaseous fuel leakage into the liquid fuel. Gaseous fuel, due to its physical state, can more easily leak past the sealing arrangements within the fuel injector and can leak into the liquid fuel or can compromise the hydraulic function of the valve actuators if it leaks from the gaseous fuel passage into the hydraulic fluid control chamber inside the fuel injector.
Accordingly there is a need for a solution for a better control of dampening the pressure pulsations at the fuel injector nozzle while controlling the pressure drop between the fuel rail and the fuel injector nozzle to prevent leakage and to control the fuel pressure at the injector nozzle before it is injected into the combustion chamber.